1. Field of the Invention
The present invention relates to an apparatus for polishing wafers and a method for polishing wafers which are employed to polish surfaces of wafers or the like that forms integrated circuits.
This application claims priority from Japanese Patent Application No. 2005-145612, filed May 18, 2005, the content of which is incorporated herein by reference.
2. Background Art
Generally, a silicon wafer of which the surface has being etched is subjected to a polishing step in which the surface is polished. A conventional polishing includes a first polishing step in which coarse bumps are smoothed away in the surface of the wafer using a wafer polishing apparatus provided with a hard polishing pad and a second polishing step in which eliminates minute pits are eliminated in the surface of the wafer using a wafer polishing apparatus provided with a soft polishing pad. Thereby, the surface of the wafer is finished to a smooth mirror surface having no strain. Since the type of the polishing pad used in the first polishing step is different from that of the polishing pad used in the second polishing step, a wafer polishing apparatus is used exclusively for each of the first polishing step and the second polishing step.
FIG. 7 is a view showing the schematic structure of a wafer polishing apparatus used in the conventional polishing method. In FIG. 7, a figure (a) is a plan view and a figure (b) is a side view thereof (see, for example, Patent Document 1).
A conventional wafer polishing apparatus includes a rotating disk 31, a polishing pad 32 adhered to substantially the entire surface of the rotating disk 31, a plurality of rotating holders 33 provided above the rotating disk 31, and a wafer mounting plate 35 fixed to each of the rotating holders 33. The rotating holders 33 are constructed so as to be able to perform a rotational movement as well as a vertical movement using a shaft 34. A plurality of wafers 36 are mounted on the wafer mounting plates 35. The symbol 37 in the drawings is an injection pipe and if needed, the wafer may be polished while an abrasive slurry 38 such as a cerium oxide based slurry is supplied from the injection pipe 37.
However, in the conventional polishing method, because the wafer polishing apparatus and the polishing pad are used exclusively for each of the first polishing step and the second polishing step, equipments and polishing materials are needed for each of the steps in order to polish the wafers. As a result, the problem arises in which production costs become high. Moreover, after the first polishing step is finished, the wafer polishing apparatus is changed and then the second polishing step is started. Therefore, the problem arises in which the polishing process becomes complicated and it takes a long time to polish the wafers.
The present invention was conceived in view of the above described circumstances and it is an object thereof to provide an apparatus for polishing wafers and a method for polishing wafers which enable to reduce equipments and polishing materials required for polishing wafers, and which can realize simplification of the wafer polishing process and reduction in the polishing time.
(Patent Document 1) Japanese Patent Application, First Publication No. S64-78758